1. Field of the Invention
The present invention relates to an apparatus for recording and reproducing a signal on and from a record medium which is suitably applied to a digital recorder capable of carrying out self-diagnosis.
2. Background
Digital recorders that can digitally record an acoustic signal or the like are now in practical use. The Digital recorders can satisfactorily carry out a signal edit or the like because there is substantially no risk that a signal will deteriorate even when signal processing such as dubbing or the like is carried out.
In digital recorders, an encoder and a decoder that are used in digital recording and reproducing incorporate therein a CPU (central processing unit) or the like to carry out complex processing. If the processor is not functioning properly, then normal recording and reproducing cannot be carried out. In particular if the encoder function is unsatisfactory, there is then the risk that the recording is invalid. To solve this problem, professional apparatus generally have a diagnostic mechanism that detects unsatisfactory function prior to the recording or the like.
According to the conventional method of detecting a malfunction, predetermined digital data is supplied to inputs of the encoder and the decoder, for example, and output data are compared with predicted data which is separately obtained by calculation or the like. A malfunction can be detected when the output data and the predicted data are not the same. Using this method substantial time would be required to carry out an exhaustive test. Therefore, there is a limit on the kinds of data that can be checked in an acceptably short period of time.
According to another test method, the output of the encoder is supplied to the input of the decoder. An arbitrary acoustic signal is then supplied from a line input, converted from an analog to a digital signal and then supplied to the encoder. Then, the encoder's output is supplied to the decoder, and a decoded output is converted from digital to analog and output to the line output. This analog signal and the signal supplied to the line input are reproduced and compared with each other in sound by a listener. In this conventional method, however, the signal supplied to the line input cannot be immediately output to the line output because of the processing time of the encoder and decoder or the like. As a consequence, a time difference occurs and sounds of the above signals cannot be easily compared. Also, there is the risk that an malfunction cannot be detected with Sufficiently high accuracy from a hearing sense standpoint.
The assignee of the present application has previously proposed an applicable diagnostic method (see Japanese laid-open patent publication No. 58-130415). According to this previously-proposed method, random data is supplied to an encoder, an encoded output is supplied to a decoder and a decoded output is converted from digital to analog. Then, a malfunction can be detected by observing the resultant analog signal.
The signal that is provided when random data is converted from digital to analog should have a frequency spectrum of constant level over the whole frequency band which can be transmitted through that system. According to the above-mentioned method, when the encoder and/or the decoder malfunction, a fluctuation occurs in the frequency spectrum. Accordingly, such malfunction can be detected by measuring such fluctuation of the frequency spectrum.
This method, however, needs a special circuit arrangement in order to observe the frequency spectrum. Also, there is the risk that malfunction cannot be detected if the malfunction occurs randomly in the encoder and the decoder.
The assignee of the present application has further proposed a digital recorder which can accurately and easily detect a malfunction (see Japanese laid-open patent publication No. 63-237263). This digital recorder is described below with reference to FIG. 1 and FIGS. 2A, 2B.
Referring to FIG. 1 of the accompanying drawings, a digital signal recorded on a tape 1 is reproduced by a reproducing head 2. A reproduced signal is supplied through a playback and equalizer amplifier 3 to a PLL (phase locked loop) circuit 4 which generates a data clock as digital data. A digital signal from the PLL circuit 4 is supplied through a selector 5 and a time base corrector (TBC) 6, which is used to cancel fluctuation of a tape transport system. The output of 6 is sent to a decoder 7, where it is de-interleaved and then error-corrected.
A signal from the decoder 7 is supplied through a muting circuit 8 to a cross-fader 9, in which it is cross-faded with a digital signal that results from converting a signal applied to a terminal 10 by an analog-to-digital (A/D) converter circuit 11. A signal from the cross-fader 9 is supplied through a digital-to-analog (D/A) converter circuit 12 to an output terminal 13. The signal from the cross-fader 9 is also supplied through a selector 14 to an encoder 15, in which it is interleaved and added with an error-correction code. A signal from the encoder 15 is supplied through a recording amplifier 16 to a recording head 17, thereby being recorded on the tape 1. The digital signal recorded on the tape 1 is reproduced and developed at the output terminal 13 and the signal applied to the terminal 10 is digitally recorded on the tape 1 by the aforesaid circuit arrangement.
In the above conventional digital recorder, a signal from a test signal generating circuit 18 is supplied through the selector 14 to the encoder 15. An output signal from the encoder 15 is fed through the selector 5 back to the time base corrector 6. The signal thus fed back and which is generated from the cross-fader 9 and the test signal from the test signal generating circuit 18 are supplied to a digital signal comparing circuit 19. A compared output from the digital signal comparing circuit 19 is supplied to an output terminal 20.
The test signal generating circuit 18 generates a digital signal having a period corresponding to a total signal processing time in which the signal is input to the encoder 15, fed back and then output from the cross-fader 9. This digital signal is supplied to the selector 14 and the digital signal comparing circuit 19.
In this digital recorder, when a digital signal having a waveform corresponding to a sine waveform of a period s that is equal to a total processing time t as shown in FIG. 2A is supplied to the selector 14 from the test signal generating circuit 18, this signal is output from the cross-fader 9 after a time t as shown in FIG. 2B through the encoder 15, the decoder 7 or the like. At that time, the test signal generating circuit 18 derives exactly the same signal delayed by one period. These signals are supplied to the digital signal comparing circuit 19 which detects whether or not these signals are coincident with each other. If the encoder 15, the decoder 7 and the like are functioning properly, the cross-fader 9 should have output exactly the same signal as that supplied to the encoder 15 with a delay time of the time t. If this signal and the signal from the test signal generating circuit 18 are completely coincident with each other, then it can be determined that functions of the respective circuits are not unsatisfactory.
The function of the digital recorder is diagnosed as described above. According to the above-mentioned apparatus, the signals can be compared with accuracy by electrical comparison. Also, the signal thus encoded and decoded and the signal with the delay time of one period are compared with each other. Such comparison of the signals can be carried out very easily. Therefore, malfunction can be detected very easily and accurately.
In a digital recorder like the digital recorder in which the decoder serving as the reproducing unit and the encoder serving as the recording unit are diagnosed in function by using the test signal as earlier noted with reference to FIG. 1 and FIGS. 2A, 2B, if the period of the test signal is made equal to the processing time of the signal processing, then circuit complexity and size increases, which also makes the digital recorder expensive.
Further, in the above-mentioned digital recorder, only the function of the decoder serving as the reproducing unit and the function of the encoder serving as the recording unit can be diagnosed. Functions of other portions of the recorder cannot be diagnosed.